Philip Hensher: Raise the curtain on another daft musical

It's not just flops and exercises in camp irony that go beyond what might be thought 'natural' subjects

There's a famous story, which originates with George Burns, of the dumb starlet who persuaded her producer boyfriend to cast her in the lead of a Broadway dramatisation of The Diary of Anne Frank. Rehearsals came and went, without ever diminishing her broad Brooklyn accent or increasing her ability to impersonate a 13-year-old Dutch schoolgirl. At the first night, the audience grew quickly restive. The Gestapo burst on stage, and one rude punter found the perfect comment. "She's behind the bookcase!" he shouted.

The story is far too good to be true. But who knows? It might happen even now. Astonishingly, the Anne Frank foundation has given permission to a Spanish theatre group to turn the famous diary into a musical. It opens in Madrid next month, when we can see exactly how naturally the heartbreaking simplicities of the diary combine with the full-on tendencies of the stage musical. Personally, I can't wait for the London transfer.

Though the whole thing has more than a whiff of The Producers about it, you don't need to reach for fictional examples to see how bizarre musical theatre can be. Mel Brooks, in inventing song and dance numbers about Hitler's rise to power "We're marching to a faster pace/Look out, here comes the Master Race" hardly exaggerated.

The history of musical theatre is littered with subjects which nobody could ever have considered a good idea. The history of musical flops exerts an unhealthy fascination over fans, some of whom would a thousand times rather sit through a revival of Bernadette than be transported back in time to the first night of West Side Story.

Some celebrated disasters have subjects which, in the barest summary, make you wonder how anyone ever thought it promising. There was Chu Chem in 1966 the first ever Buddhist-Jewish musical, set in 10th-century China and including some sumo wrestlers for good luck. Odd corners of famous American political lives seem to allure the contrivers of musical theatre. There was Teddy and Alice in 1987, about Theodore Roosevelt and his daughter (77 performances).

There was Ben Franklin in Paris in 1964, a relative success at over 200 performances. Obviously rubbish subjects along the lines of the fondly-remembered Norwegian catastrophe, Which Witch, Bernadette or, reaching back a little further, Into The Light an attempt to demonstrate the authenticity of the Turin Shroud through song and dance have created a peculiar sub-genre. There is no shortage of musicals which deliberately revel in the bad taste of adding singing and dancing to subjects which need none.

But it's not just flops and exercises in camp irony which go far beyond what you might think of as the musical's natural subject matter. When you think of the great masterpieces of the musical, you start to wonder whether there is, in fact, any natural subject matter there at all. My Fair Lady is unpromisingly about phonetics; The Pajama Game about trade union rights; Lady in the Dark is about psychoanalysis; Hairspray about the civil rights movement.

Stephen Sondheim has made a wonderful career out of the most unlikely topics. Pacific Overtures is about imperialist moves towards Japan in the 19th century; Sunday in the Park with George about pointillism; Assassins about people who tried to kill various American presidents. Later this month comes a splendid film of his gruesome masterpiece, Sweeney Todd, about a legendary serial killer. We're a long way from No, No, Nanette!

But perhaps the freedom which the musical, at its best, used to exult in is most apparent not in stage productions in the West, but in the wonderful productions of Bollywood. It sometimes seems as if there is no subject, however grave, which can't be amplified with an expressive song or even a dance routine; the imperial tensions enacted through a cricket match in Lagaan, or the quite recent race riots in Mumbai. Border tensions between India and Pakistan in Lakshya; freedom fighters in Dil Se. That last one must have the most spectacular dance routine ever committed to film, and the seriousness of the film's purpose seems hardly diminished at all.

I don't give much for the chances of Anne Frank: the Musical, however. The idea that music might be added to such a story seems vaguely improper; the idea that it might contain anything in the way of a dance routine, to us, is obviously an obscene one.

It wouldn't always have seemed so, and it wouldn't seem so everywhere in the world even now. The fact is not that we have grown more serious, but less so. We don't grant areas of artistic expression, such as dance, the right to seriousness at all. The limitations are too strong; the conventions which are dictated by such a subject are, at present, guarantees that nothing surprising or insightful could come from the collision. It's not that we take these subjects seriously; it's that we are unable to take art seriously enough.